NEAR is killing me.

[Panzerbeard]

So, I've been playing KSP for quite a while now, I wouldn't say I'm great at it, but I generally know my way around a rocket- but I've always been flying with stock aerodynamics. I thought I'd start a new career save with NEAR installed, and now I just can't get into orbit with anything approaching efficiency, grace, and non-explodeyness. I've gathered that high CoM and low CoL is favourable and that I want a lower TWR than stock (I aim for around 1.3-ish). I also know that I need to follow a shallower ascent path than I normally would. Knowing all that, however, I still can't get into orbit consistently.

As far as I can tell this should be able to get into orbit perfectly well; it's got more than enough dV, the centre of mass is above the CoL in each stage, I have as much control authority as I can give it (I don't have reaction wheels unlocked yet, both engines are T45s with gimballing, though). However, after I start my initial tilt to about 5 degrees east after launching, it'll slowly tilt over to horizontal and I can't keep it pointing up high enough to stop the rocket falling before I leave the atmosphere.

Other designs just fail entirely or wobble around so much that if I do end up in a stable orbit I've wasted a lot of fuel and am nowhere near equatorial. I see that I'm going to have to completely relearn rocket design and flight, but any advice would be appreciated

Edited November 6, 2014 by Panzerbeard

[NathanKell]

Try a smaller initial tilt, perhaps?

Also, don't start your initial turn until about 110m/s (I'd say 100, but 1.31 starting TWR is quite low).

[Alshain]

Or wait a little longer before beginning the tilt. (higher altitude & speed). Every rocket is different and real aerodynamics just highlight that fact.

Center of Lift on a rocket doesn't tell you a whole lot, btw. The main thing is to keep your CoM lower or it will flip end over end. Your second stage looks pefect, the first one, it looks a little high.

If your CoM is higher, don't tilt over right off the launch pad, wait till 3-4k, maybe even more.

Edited November 3, 2014 by Alshain

[Tex_NL]

Or wait a little longer before beginning the tilt. (higher altitude). Every rocket is different and real aerodynamics just highlight that fact.

Center of Lift on a rocket doesn't tell you a whole lot, btw. The main thing is to keep your CoM lower or it will flip end over end. Your second stage looks pefect, the first one, it looks a little high.

If your CoM is higher, don't tilt over right off the launch pad, wait till 3-4k, maybe even more.

Sorry but this is not true. Just as planes you want you CoM IN FRONT of your CoL. Ashflare's CoM and CoL are exactly where they should be.

[Alshain]

Sorry but this is not true. Just as planes you want you CoM IN FRONT of your CoL. Ashflare's CoM and CoL are exactly where they should be.

Nope. Doesn't matter, you aren't lifting using wings. In fact you don't need the winglets if you are using thrust vectoring (I can't tell if that is the LVT-30 or LVT-45) then you have no lift.

I'm really not sure how you would get your CoL that far forward with just winglets anyway unless you just put them on the tip, which I can't imagine happens often. Even for beginners if you've ever seen a picture of a rocket or missile you would know better.

Edited November 3, 2014 by Alshain

[regex]

For a stock sized solar system, I'd start my tilt somewhere around 65~75m/s and follow the top of the prograde marker, not the middle. TWR is perfectly fine for a starting stage; you're going to be shedding that first stage like an old coat so you don't want to be turned over too far when you start on the second with its similar TWR. This one ... maybe start your turn at 80m/s and, again, follow the top of the prograde marker until you're nearly out of the second atmosphere band, then shift to the bottom. Once you're into the third atmosphere band, go horizontal and build up the speed for orbit.

[Tex_NL]

Nope. Doesn't matter, you aren't lifting using wings. ...

All true. I slightly misread your edited post. In your un-edited version you said he needed his CoM lower than his CoL.

I've tried to replicate Ashflare's design as best as I could to look what MechJeb would make of it under NEAR. MechJeb does make it to orbit the control surfaces are flapping all over the place the entire flight. It is not the most stable design.

I played around with it a bit and got slightly better results by removing one of the three tanks in the upper stage and replacing the bottom stage LV-T45 with a slightly more powerful LV-T30. Since you have more than enough control surfaces you do not need the gimballing.

Edited November 3, 2014 by Tex_NL

[Alshain]

All true. I slightly misread your edited post. In your un-edited version you said he needed his CoM lower than his CoL.

I've tried to replicate Ashflare's design as best as I could to look what MechJeb would make of it under NEAR. MechJeb does make it to orbit the control surfaces are flapping all over the place the entire flight. It is not the most stable design.

You might have misread, I said CoM needs to be lower, not lower than CoL, just lower on the rocket in general. I don't think I said that pre-edit either, I only added "& speed". In any case, it doesn't matter. We are on the same page now.

[NathanKell]

No, CoM never needs to be lower, unless you need more control authority (which, if you start the turn at the proper time/speed, you should not). You want the CoM as high as possible in a rocket, always, again unless it becomes too stable.

[Tex_NL]

You want the CoM as high as possible in a rocket, always, again unless it becomes too stable.

This does actually make a lot of sense. I'm pretty sure everybody has tried to balance a hammer on one finger at least once in their lives. Try balancing it with the head up (high CoM) and it is pretty easy. You only need some gentle corrections to keep it balanced. And even large movements are easily corrected.

Now try it with the head down (low CoM) and the much lighter handle up. Suddenly it becomes much more difficult. It takes large and strong movements to keep it balanced.

[Empiro]

You can definitely have issues launching rockets that are really top heavy (in the form of rockets snapping in half), but in this case, it looks like you're turning too much too early. There's always a sweet spot for when you turn and how much, but it greatly depends on the design. For small rockets with a low TWR, as you have here, you'll want to turn a smaller amount and later.

Once piece of advice -- if you find yourself too shallow or too steep, I like to use trim settings to correct the trajectory. It lets you push things slightly in one direction or the other without lots of tapping, and greatly lowers the risk of structural failure.

[Leszek]

There is a lot of arguing going on but there is one simple piece of advice that is most important.

When I started with NEAR I tried fins and verners and I extra SAS modules. They help but I don't need them anymore. Ignore the COM and take the winglets off, you should still be able to get into orbit just fine reliably with anything that is remotely aerodynamic.

The trick is this, if you point the rocket too far off the direction you are going, you are going to flip out and lose control. All you have to do is keep your rocket inside the circle that is your velocity vector. That is it. Also you can judge how close you are by watching how much control SAS is putting in to counter forces.

Everything else is learning when to start your gravity turn (and I mean a real gravity turn, I have done it without SAS and no control inputs for something like a dozen seconds on end.) so that your velocity vector doesn't fall too fast.

What I do is start my GT at 75 M/s. I like speeds because it auto compensates for different rocket TWR's within limits. I Normally go for a starting TWR of 1.25, but anything in the ballpark should work. I tilt to 85 degrees when I get to 75 M/S. After that I follow the velocity vector down until 25 degrees. I try to aim to be there after 20,000 meters. So if my velocity vector is falling faster, I will lag behind it but still in the circle to slow it down. After about 30 KM, you can point the rocket much more aggressively. After that every time my Apoapsis is 10 km higher I aim 5 degrees lower. So at an apoapsis of 30 KM I am at 20 degrees. At 40 I am at 15 degrees and so on to horizontal at an apoapsis of 70KM. You can get to orbit with 3600 DV. (And that is with a wide margin, last rocket I sent up got there with 109 DV to spare.)

[NathanKell]

It's also worth noting that, if you're relying on control surfaces for control, you really won't get much authority in the upper atmosphere, let alone the near-space region (30+ km). Use engines with gimbal.

[Starman4308]

It's also worth noting that, if you're relying on control surfaces for control, you really won't get much authority in the upper atmosphere, let alone the near-space region (30+ km). Use engines with gimbal.

Or moar reaction wheels/RCS.

But since most engines are gimballed anyways (with the notable exceptions of the aerospike, the LV-T30, the PB-ION, and a few of the really dinky engines), just use those.

[KerikBalm]

I've gathered that high CoM and low CoL is favourable and that I want a lower TWR than stock (I aim for around 1.3-ish). I also know that I need to follow a shallower ascent path than I normally would. Knowing all that, however, I still can't get into orbit consistently.

FAR is even worse

NEAR is near perfect realism vs gameplay balance, IMO

But why do you think TWR should be lower?

In stock, you don't want a TWR of over 2.0, because of soup for atmosphere, and really low terminal velocities.

With NEAR, your terminal velocity (if you built the rocket right) should be really high, that means to travel at optimal ascent speed (for a vertical climb, granted its over simplified), you need to go a lot faster, and you need a higher TWR to get to the speeds you want to go.

More TWR, get at least 80 m/s before you start your turn.

[Starman4308]

FAR is even worse

NEAR is near perfect realism vs gameplay balance, IMO

But why do you think TWR should be lower?

In stock, you don't want a TWR of over 2.0, because of soup for atmosphere, and really low terminal velocities.

With NEAR, your terminal velocity (if you built the rocket right) should be really high, that means to travel at optimal ascent speed (for a vertical climb, granted its over simplified), you need to go a lot faster, and you need a higher TWR to get to the speeds you want to go.

More TWR, get at least 80 m/s before you start your turn.

It's because, unlike in stock, where low ascent is limited by the souposphere and you design to hit terminal velocity, in FAR/NEAR, you are limited by your rocket experiencing an unplanned departure from controlled flight regime, rapid unplanned disassembly, and high-speed lithobraking. In order to keep your rocket under control in low atmosphere, you've got to limit your launch TWR. Also, because aero drag is so low, you build up speed a lot faster than in stock, even with much lower TWR, reducing gravity losses.

[Leszek]

I made a video of a copy of your rocket as close as I can make it. No Fins.

I note that your rocket is a bit touchy, easiest fix is to move the parachutes to the bottom of that stage. After engine cut off I did lose stability, I didn't try that hard to keep it stable and the reaction wheels in the stayputnik aren't up to the challenge. If I had throttled down for the second stage I would have been able to keep it and the whole thing would have looked better for the coasting to orbit. The video ends with a 100 KM Apoapsis.

Sorry for the picture quality, it was my first game screen capture and I had to figure it out on the fly, I might try to fix it later. (Quality fixed itself, too bad the sound is not so good.)

Edited November 4, 2014 by Leszek
P.S.

[Alshain]

FAR is even worse

NEAR is near perfect realism vs gameplay balance, IMO

But why do you think TWR should be lower?

In stock, you don't want a TWR of over 2.0, because of soup for atmosphere, and really low terminal velocities.

With NEAR, your terminal velocity (if you built the rocket right) should be really high, that means to travel at optimal ascent speed (for a vertical climb, granted its over simplified), you need to go a lot faster, and you need a higher TWR to get to the speeds you want to go.

More TWR, get at least 80 m/s before you start your turn.

Good luck turning it. If you go too fast the low atmosphere makes it hard to turn because the faster are, basically the slower you need to turn to avoid control issues. Before you know it your at 50km and you haven't finished your gravity turn, you will never reach maximum horizontal speeds before orbital heights (assuming around 70k), and you have to waste all your fuel circularizing which is the worst most inefficient thing you can do.

[Panzerbeard]

Many thanks for the replies, all; sounds like my problem mostly lies with my gravity turn and going overboard with fins , I figured it best to get the extra control authority since I don't have reaction wheels yet, but they just wobble the craft around far too much with SAS on, and for some reason I seem to get some rolling out of nowhere when I turn it off? Either way, I guess that'd be fixed by removing the fins anyway, so thanks for the suggestion of removing them. I'll also build up a little more vertical speed before turning.

I'm dreading airplane/spaceplane testing. I fear I may run out of kerbals.

It's also worth noting that, if you're relying on control surfaces for control, you really won't get much authority in the upper atmosphere, let alone the near-space region (30+ km). Use engines with gimbal.

Yeah, I always do use gimballed engines for my upper stages, unless I've got a lot of torque. I generally add the fins more for stability than for extra control for the most part.

I made a video of a copy of your rocket as close as I can make it. No Fins.

I note that your rocket is a bit touchy, easiest fix is to move the parachutes to the bottom of that stage. After engine cut off I did lose stability, I didn't try that hard to keep it stable and the reaction wheels in the stayputnik aren't up to the challenge. If I had throttled down for the second stage I would have been able to keep it and the whole thing would have looked better for the coasting to orbit. The video ends with a 100 KM Apoapsis.

Sorry for the picture quality, it was my first game screen capture and I had to figure it out on the fly, I might try to fix it later. (Quality fixed itself, too bad the sound is not so good.)

That was extremely helpful, thankyou for that. I'm curious, though, what is it about the parachute placement that's causing problems? Is it just the additional drag acting too close to the CoM?

[Leszek]

Ignore the parachute placement. I was thinking aerodynamically and that means put them back farther. Like a shuttlecock. But that is an upper atmosphere stage so probably not much difference. By weight you want it forward. My bad.

Glad the video helped.

If you want to do aeroplanes and spaceplanes, you want FAR. I don't do that so I just use NEAR. I tried to do aeroplanes with NEAR the SPH can lie to you about where your COL is and other variables. Big headache.

The good news is that the aerodynamics between them are similar. It is the same code after all. Mostly it is the scary looking FAR window that scares people off I think. It isn't worth the effort to change from one to the other unless you are doing space planes though.

Edited November 4, 2014 by Leszek
Added more info.

[Empiro]

Hmm, if you're keeping SAS on after you start your turn, then that's something you shouldn't be doing. I always keep my SAS on until 50-70 m/s, start my turn (when exactly and how much depends on TWR and size of rocket), and then turn SAS off. Then I make minor adjustments using trim settings and aim for 45 degrees at 10km.

I've found that I only need reaction wheels in the upper stage if I'm using a probe core (with very little torque) or if I have a very large upper stage. During the ascent, stabilizers and engine gimbals generally seem to be enough.

In FAR, I've noticed that if you don't have fins, then your rocket's coefficient of drag is through the roof in the analysis screens. I don't know if that's just a quirk of FAR and you don't really need them, but I've never had any issues using stabilizers at the bottom of my rocket.

[Leszek]

If you are using fins, you should turn down their control authority and then you can keep using SAS. Without fins SAS helps a lot.

[Panzerbeard]

Ignore the parachute placement. I was thinking aerodynamically and that means put them back farther. Like a shuttlecock. But that is an upper atmosphere stage so probably not much difference. By weight you want it forward. My bad.

Glad the video helped.

If you want to do aeroplanes and spaceplanes, you want FAR. I don't do that so I just use NEAR. I tried to do aeroplanes with NEAR the SPH can lie to you about where your COL is and other variables. Big headache.

The good news is that the aerodynamics between them are similar. It is the same code after all. Mostly it is the scary looking FAR window that scares people off I think. It isn't worth the effort to change from one to the other unless you are doing space planes though.

It's the mach effects that put me off FAR, mostly. I'll probably move on to it at some point, once I'm comfortable enough with NEAR, but I'm not a big aircraft guy, really, I dabble occasionally and I'll probably build a couple to use as test beds for contracts, and for the location-based contracts from Fine Print, but I'm mostly rocket-focused. Maybe a basic spaceplane for the sake of trying out the shiny new cargo bays. As long as aircraft can work within reason I'm fine using NEAR for the time being

[Jovus]

Funnily enough, the Mach effects make re-entry easier, because they greatly increase drag in the higher levels of the atmosphere.

[tater]

It's funny, I've been using FAR for a while (started playing in august, so maybe a couple months with FAR) and I was assuming that it must only be noticeable for aircraft (which I don't do at all in KSP). I've honestly not noticed much difference at all between FAR and stock (and that's with KIDS as well).

What I have seen a few time is with DRE, really. SRBs used for sounding rockets for contracts… I'll burn off the chutes on ascent, lol. I ended up loading them with science gear to slow them down (they were even burning up inside a fairing (PF).